We are investigating the molecular mechanism by which enzymatic activation of human Hageman factor (HF) proceeds. We have shown that the first step involves Hageman factor autoactivation when it binds to certain negatively charged surfaces. One of its activated forms, HFa, digests native HF to form more HFa and further digestion of HFa yields an active fragment, HFf, which retains activity. When prekallikrein is converted to kallikrein by HFa or HFf, kallikrein further digests the remaining unactivated HF and HMW-kininogen is a cofactor for this reaction. We will examine the kinetics of HF activation when one or more of these components is left out to better delineate the role of each. We will determine the chain structure of HFf and try to pin-point the site of HFa cleavage required for its formation. Cleavage of HFa by autodigestion (HFa), kallikrein and kallikrein plus HMW-kininogen will be compared and the possible formation of more than one molecular species of active enzyme will be examined. We will continue our studies on the role of the light chain derived from HMW-kininogen as a coagulation cofactor and attempt to distinguish that portion which binds prekallikrein from that which binds to initiating surfaces. We will also further define te Hageman factor dependent fibrinolytic pathway by examining the kinetics of plasminogen cleavage in whole plasma.